Growing plants one on top of another gets the most out of every square inch of
your outside space. Sarah Raven shows you how.

I am not the sort of gardener who sits outside under a tree peacefully reading a book. I want my garden to be beautiful, but I also want it to produce food and flowers. I’ve spent a great deal of effort over the past few years trying to make sure we get the best possible harvest from every little bit. Whether you garden in a few containers or rolling acres, you can maximise your square-inch productivity by following two very simple principles.

A large proportion of the plants you grow should be cut-and-come-again – so you can harvest all you like on a Friday and by the following Friday the same plants are there to be harvested again. This is not so much about parsnips, carrots or potatoes, but chards, salad leaves and other continuous croppers. With flowers, think not so much of peonies or a bunch of lilac, but more of sweet peas, cosmos or sunflowers. These are all massive producers, and the more you pick, the more will follow.

Another simple way to maximise production is to plant at different levels in the soil – in a sort of lasagne technique – with bulbs or tubers, as well as annuals or perennials, in layers on top of one another. Miraculously, with the right plants, the deepest almost always find their way around those planted on top. If you have ever split open a pot planted with bulbs, you’ll have observed this useful habit they have of being able to bend around any obstruction put over their heads. Whether it’s narcissi, tulips or alliums, it doesn’t seem to bother them. Their flowering stems may be a little shorter than if planted nearer the soil surface, but they’ll still give you a fine performance.

I have three main productive areas at Perch Hill, which I expect to pump out produce. All three have different layers, so that I have plants to look at and harvest from early in the year until late.

The first area is a bed about 4ft wide and 60ft long on the eastern end of a bank that surrounds the garden and cookery school. This started out with just artichokes, planted five years ago. Last autumn, we thinned them out a little so we could fit dahlias in between. The dahlias (pot-grown tubers at young plant stage), were placed just below the soil surface and mulched deeply to insulate them through the winter. Then, using a bulb planter, we added 100 alliums spaced around the dahlias and artichokes, but put in as deep as we could – about six inches. The various different varieties flower one after another.

Allium rosenbachianum flowers first in early May, followed by 'Purple Sensation’ for their deep purple pom-poms later that month, then the vast sparkler head A. schubertii, then A. cristophii which takes us through June, finishing with A. sphaerocephalon for July, even into August. I should now be able to pick the odd bunch of alliums from this bed for four months, as well as harvest seedpods to dry for autumn and Christmas arrangements.

That’s not all. The globe artichokes in this bed (roughly 24 plants) comprise three different varieties that crop quite neatly in succession, and the foliage remains above ground all year. It’s looking winter-weary right now, but soon new leaves will shoot from the crowns, the plants will perk up and the foliage will look good as a backdrop to the alliums. The artichokes themselves start to crop from the end of May, starting with the early variety 'Violetta’, followed by 'Green Globe’, finishing with 'Gros Vert de Laon’. As each plant stops forming the tasty green flower buds, we cut them right to the ground, leaves and all, which kick-starts them into a whole new season. They then roll around again, 'Violetta’, 'Green Globe’, and 'Gros Vert de Laon’, to give a light harvest from late August into October.

That’s still not all. As the artichokes are cut, the dahlias take centre stage, their flowers standing out against the fresh, new silvery artichoke foliage. The great thing about dahlias is they look good and give me flowers to pick until at least November. There’s now a triple harvest in this bed and three times the amount to look at, yet by using the depth of soil rather than the surface, it never seems overcrowded.

Strictly cut flowers

In the cutting garden, I also have three rectangular beds packed with different flowers. To take one as an example, in the autumn, I planted it up with a range of different narcissi at 8in deep, with hyacinths around the outside at about 6in. Dahlias went in last, just below the soil surface.

The blue hyacinth 'Peter Stuyvesant’ starts in March, along with the scented, multi-headed, cut flower narcissi 'Avalanche’. The narcissi flower in succession until May – next is the petite and pretty 'Silver Chimes’ with one of the best-ever scents. Then comes 'Geranium’, which often has seven or eight flowers to each stem and so only needs five stems to fill a jug; then 'Actea’; and finally the classic 'Pheasant’s Eye’, famously one of the last to flower in late spring. Even though not they are not multi-headed, these last two have such wonderful scent and such a long vase life, it’s mad not to grow them.

Once the narcissi are over, I feed them with fish, blood and bone and let the leaves die back for six weeks, before I clear the foliage to allow the dahlias to push through. I have to watch for slug damage: in a wet spring like the last one, I cover each dahlia crown with a cloche or copper ring to protect the first shoots that emerge into the still-dense daffodil foliage.

Flowers with my veg

My final area of plant layering is in the veg garden. There, we plant tulips 6in deep in autumn and over-plant them with winter lettuce or kale. I select tulips with longevity. The Viridiflora types can flower for years, so 'Artist’, 'Pimpernel’, 'Groenland’ and 'Spring Green’ are all ideal. Over their heads can go lettuce, such as 'Valdor’, 'Unico’ or 'Green Oak Leaf’, or one of the hardy winter salad leaves, such as 'Mizuna’ and 'Red Giant’ mustard, or the cucumber-flavoured herb, salad burnet.

Some of the parrot tulips are also very durable, as is the giant and elegant 'Menton’. I use this apricot-pink tulip to under-plant my 'Redbor’ kale. I also extend this idea into May: beside the path on the salad bank I have Dutch iris planted beneath cut-and-come again lettuce. The iris seem to get bigger and better every year. I’ve gone for two lettuces there again this year, 'Cocarde’ and the stalwart 'Green Oak Leaf’.